1. Technical Field
This invention relates to a planetary gear device having a backlash adjusting mechanism which is capable of adjusting backlashes between planetary gears and a sun gear and between the planetary gears and an internal gear by twisting divided-type carrier parts relatively with each other.
2. Prior Art Description
As like as other gear devices, planetary gear devices are also provided with backlashes between component gears in the consideration of interference of gears due to manufacturing errors, assembling errors, thermal expansion during operation and the like. This means that an input-side gear and an output-side gear have a play corresponding to the backlashes with respect to fixed gears with which they are engaged.
Several methods have been proposed to adjust or eliminate the backlashes between gears, one of which is such that a carrier supporting planetary gears is divided into two parts, planetary gears adjacent to each other in a circumferential direction are supported by the different divided carrier parts, and the both carrier parts are twisted relatively with each other to realize an engagement condition wherein the adjacent gears regulate the plays corresponding to the backlashes of the other gears with respect to each other.
A planetary gear device applied with the above method is disclosed in Japanese Utility Model Laid-open No. Hei 2-38551 and Japanese Patent laid-open No. Hei 2-283939, both assigned to the same assignee of this invention, for example. A backlash-elimination mechanism of the planetary gear device having relatively-rotatable carrier parts that are disclosed in the above publications will be explained briefly.
As shown in FIGS. 5 and 6(A), a planetary gear device 200 of this type is provided inside a cylindrical casing 202 with a first and a second carrier parts 205 and 206 of disk shape which are rotatably supported by ball bearings 203 and 204, respectively. Four planetary gears 211-214 are sandwiched between the first and second carrier parts 205 and 206. The first carrier part 205 has planetary shafts 221 and 223 of the planetary gears 211 and 213 positioned along a diametrical direction which are fixedly connected thereto by fastening bolts 231 and 233 and support the planetary gears 211 and 213, respectively. Likewise, the other carrier parts 206 has planetary shafts 222 and 224 of the remaining planetary gears 212 and 214 also positioned along a diametrical direction which are fixedly connected thereto by fastening bolts 232 and 234 and support the planetary gears 212 and 214.
The first and third planetary shafts 221 and 223 fixed to the first carrier part 205 is slightly movable with respect to the second carrier part in a circumferential direction about a device axial line 200a, while the planetary shafts 222 and 224 fixed on the second carrier part 206 is slightly movable with respect to the first carrier part 205 in a circumferential direction about the device axial line 200a.
Provided now that, as shown in FIG. 6(A), there occur backlashes in the clockwise direction of the planetary gears 211-214 (output element) with respect to the sun gear (input element). The both carrier parts 205 and 206 of this condition are twisted in opposite circumferential directions, which results in realizing an engaging condition as shown in FIG. 6(B). Then, the carrier parts 205 and 206 of this condition are fastened together by fastening bolts 231-234, so that a condition in which the backlashes are eliminated can be realized. Namely, in this condition, since the plays of the planetary shafts 221-224 in the clockwise direction are restricted by opposite tooth flanks of the planetary gears 212 and 214, the backlashes are eliminated.
In the thus constituted planetary gear device 200, when the carrier parts 205 and 206 are twisted relatively at the side of the carrier part 206, for example, in order to adjust backlashes, the carrier part 206 must be twisted with holding the opposite-side carrier part 205 not to rotate, prior to fastening of the fastening bolt 234. It is required for this operation to apply the carrier parts with forces from both sides of the axial direction (namely, from input and output sides). This operation cannot be carried out after the planetary gear device is mounted on a motor housing or other members.
Further, the carrier parts 205 and 206 are supported separately by the different ball bearings 203 and 204, and therefore, when the both carriers 205 and 206 are rotated relatively, misalignment of center axes between the carrier parts is likely to occur, and an accurate assembly cannot be expected, which is a problem.
An object of this invention is to provide a planetary gear device having a backlash adjusting mechanism which is able to a void the aforementioned defects.